THE EVOLUTION OF COSMIC-RAY MEDIATED MAGNETOHYDRODYNAMIC SHOCKS - A 2-FLUID APPROACH

We study the shock structure and acceleration efficiency of cosmic-ray mediated MHD shocks both analytically and numerically by using a two- fluid model. Our model includes the dynamical effect of magnetic field s and cosmic rays on a background thermal fluid. The steady state solu tion is derived by following the technique of Drury & Volk (1981) and compared to numerical results. We explore the time evolution of plane- perpendicular, piston-driven shocks. From the results of analytical an d numerical studies, we conclude that the mean magnetic field plays an important role in the structure and acceleration efficiency of cosmic -ray mediated MHD shocks. The acceleration of cosmic-ray particles bec omes less efficient in the presence of strong magnetic pressure since the field makes the shock less compressive. This feature is more promi nent at low Mach numbers than at high Mach numbers.